Among “multiple access” schemes by which a plurality of users can simultaneously communicate with each other, a CDMA (Code Division Multiple Access) scheme having excellent frequency use efficiency has been commercialized by a plurality of methods. Among these schemes, particularly, one scheme of a global standard IMT-2000 defined by International Telecommunication Union (ITU) is W-CDMA (Wideband-Code Division Multiple Access). Mobile communication terminals using the above-described access scheme have been commercialized. Also, a next-generation mobile communication standard called LTE (Long Term Evolution) has been formulated.
A communication scheme or a data format related to the above-described W-CDMA or LTE scheme has been studied by 3GPP (3rd Generation Partnership Project), and standardized as a global standard. Mobile communication terminals and base station devices should conform to the above-described standard.
Test content and measurement items for checking the conformance to the 3GPP standard are defined as a conformance test. A test system for performing the conformance test is provided. The conformance test includes an interference wave test which verifies the performance of interference wave immunity of a mobile communication terminal and a transmission test which verifies the effect of a spurious component included in a transmission wave from the mobile communication terminal.
In an interference wave test, the conformance to the standard is checked by transmitting a pseudo base station signal combined with an interference wave from a test system including a pseudo base station to the mobile communication terminal and checking/verifying whether the mobile communication terminal returns an accurate response signal to the pseudo base station signal. When the interference wave is combined with the pseudo base station signal, a component corresponding to a frequency band of a carrier is excluded from a signal of the interference wave generated by a signal generator so as to prevent a carrier component from being affected by a spurious component of the interference wave, and the interference wave and the pseudo base station signal are combined.
In a transmission test, the conformance to the standard is checked by transmitting a pseudo base station signal from the test system including the pseudo base station to the mobile communication terminal and measuring a spurious component included in a signal returned from the mobile communication terminal. Since a signal component corresponding to an original response signal is outside a measurement target when the spurious component is measured, the spurious component is measured by excluding a component corresponding to a frequency band of the original response signal from the returned signal.
In the interference wave test and the transmission test as described above, a function called a band stop filter which excludes a component of a specific frequency band is necessary. In these tests, it is necessary to respectively verify signals of various frequency bandwidths defined by the 3GPP standard in a frequency band (for example, from 500 MHz to 4 GHz) used for mobile communication. Hereinafter, a frequency band used in mobile communication is called a communication frequency band.
Recently, it is necessary to add/change a frequency band range capable of being verified even for the test system since a specification range is extended such as formulating an LTE standard including a technical specification of HSPA (High Speed Packet Access) or the like serving as a higher standard of W-CDMA and therefore an available frequency band is also added/changed. That is, there are various frequencies and bandwidths to be used for communication by frequency band allocation of a communication standard or communication provider. Thus, a band stop filter of the test system should adapt to various frequencies and bandwidths.